The pulmonary artery catheter (PAC) is a commonly used device that provides hemodynamic data to guide care of the critically ill, such as patients with acute lung injury or the acute respiratory distress syndrome (ARDS/ALI). Clinicians believe PAC use improves decision-making and patient outcomes but evidence is lacking and recent data suggest the PAC may increase mortality as well as considerably increasing costs. In response, the NHLBI funded a large multicenter trial (Fluid And Catheter Treatment Trial (FACTT) (N01-HR-46054-46064)) where ARDS/ALI patients will be randomized to receive a PAC or the less invasive central venous catheter (CVC) and to receive a liberal or conservative fluid management protocol in response to data provided by the PAC or CVC. The primary end-point will be in- patient mortality. We propose to complement FACTT with a concurrent economic analysis of the PAC. Our aims are to: 1.) compare differences between study arms in long-term survival, quality of life, and quality-adjusted survival; 2.) compare differences between study arms in acute care and long-term costs; 3.) calculate the cost- efficacy of PAC use (i.e., the balance of costs and effects under the controlled environment of the FACTT trial), and; 4.) estimate cost-effectiveness under more "real-world" conditions and produce life-time cost-effectiveness ratios, thereby facilitating comparison of our results to other cost-effectiveness analyses. We will achieve Aims 1-3 by augmenting FACTT data collection with detailed information on hospital costs, extended survival follow- up for a minimum of one year, and post-discharge patient interviews to determine quality of life and resource use in the first year. We will achieve Aim 4 by constructing a microsimulation model first calibrated by results from FACTT and published data on life-expectancy and costs and then adjusted to reflect the broader patient case-mix and clinical effects of PAC use in routine clinical practice. We will use patient-level data from the King County Lung Injury Project epidemiology study (NHLBI HL-96-014) to adjust case-mix and patient-level data from a large pragmatic trial of PAC use in the United Kingdom to adjust the clinical effects of PAC use. The results of our proposed adjunct to FACTT will substantially amplify the value of the data being collected and provide, for the first time, robust estimates from randomized data of the economic effects of the widespread application of this important technology.